1. Field of the Invention
The invention relates to a protective device for a repeatedly rechargeable electrochemical battery with a battery housing, the protective device having at least one switching element which can be activated by a detector element and which is designed or adjusted to prevent recharging and/or discharging of the battery in an unallowable operating state thereof.
2. Description of Related Art
In electrochemical batteries, for example, due to excess charging or a short circuit between the terminal contacts of the battery housing, the pressure can rise within the battery, which can lead to a deformation of the battery housing which is so great that chemicals emerge especially in gaseous form.
It is known from published European Patent Application Nos. EP A 0 322 112, EP A 0 360 395 and EP A 0 370 634 that electrochemical batteries can be provided with a switching element which, when a certain still tolerated boundary deformation of the battery housing is exceeded, preferably, irreversibly separates an electrical terminal contact from the pertinent electrochemically active electrode in order to prevent further deformation of the battery housing. The battery housing comprises an electrically conductive cylindrical housing section which is closed on the face and which makes contact with an electrode, the face the plate-shaped switching element being attached centrally from the outside by means of electrically insulating cement. In its base position, the electrically conductive outside edge of the switching element forms an electrical connection between the housing section and the electrical terminal contact which projects to the outside and which is located in the center of the switching element. When the pressure increases within the battery housing, the face of the housing section which acts as the detector element curves to the outside, interrupting the contact between the housing section and the outside edge of the switching element, and thus, between the one electrode and the terminal contact. Typical applications of these switching elements are type "D" standard batteries. The curving of the face side, starting from which the switching element interrupts the electrical contact, in this case, is 0.76 mm to 1.8 mm. For curvatures exceeding 1.8 mm, escape of chemicals from the interior of the battery housing can usually be expected.
Published European Patent Application No. EP A 0 470 726 discloses an electrochemical battery with a cylindrical battery housing and a pressure membrane as a detector element which is integrated on the face side in the battery housing and which deflects when the pressure rises in the interior of the battery housing, by which a plate-shaped switching element centrally connected to the pressure membrane reversibly or irreversibly interrupts the electrical contact between an electrode and a terminal contact of the battery.
Published European Patent Application No. EP A 0 674 351 discloses an electrochemical battery with a battery housing which comprises a cutting device which can be actuated by a pressure membrane and which irreversibly cuts an electrical lead when a pressure limit within the battery housing is exceeded and which connects a terminal contact of the battery with an electrochemically active electrode.
Also, when using a switching element which interrupts the electrical connection between the terminal contact and the respective electrochemically active electrode, when a certain pressure is exceeded within the battery housing, it is possible for the pressure to continue to rise and ultimately for the chemicals to escape from the battery housing or for it even to explode. For this reason, it was proposed (for example, in Published European Patent Application Nos. EP A 0 364 995, EP A 0 573 998 or EP A 0 739 047) that a pressure membrane which actuates the switching element and which is integrated into the battery housing be provided with a bursting area via which chemicals can escape from within the battery housing after activation of the switching element and after the pressure continues to rise.
The protective devices listed in the aforementioned prior art for electrochemical batteries are not suitable for use as part of implantable devices because, for this purpose, especially high demands must be satisfied, particularly with respect to safety and reliability together with simultaneous reduction of all dimensions as much as possible. Contamination of the surrounding tissue with toxic substances and endangerment of the implant wearer by battery malfunction must be precluded under all operating conditions.